Large vehicles such as buses, trucks and off road vehicles use external rear view mirrors that allow the driver to look both laterally and to the rear of the vehicle. Often these external rear view mirrors are mounted on vertical poles that are located on the outside of the vehicle. These mirrors are generally shaped as elongated rectangles. Mirrors of this type contribute to drag and wind noise when the vehicle is in motion.
Although it is an advantage to provide an external rear mirror with electric actuators, there are also drawbacks. Electric actuators allow the driver to adjust the mirrors tilt and pan angles from inside the vehicle. However, the actuators themselves and the housings and mountings that they require add to the cost, complexity and weight of the overall mirror assembly. The final assembly process itself is complicated by the actuator's, their mountings and housings.
The above matters are further complicated by the fact that some external rear view mirrors comprise a combination of a flat mirror together with a curved mirror. The flat mirror is usually the larger of the two and provides a conventional flat reflective surface. The flat mirror may sometimes combined with a smaller convex mirror that provides a wider but distorted field of view. Thus, mirror assembly may comprise a pair of mirrors, a pair of actuators, a pair of actuator mountings etc combined within a single housing. Having distinct non-identical upper and lower mirrors makes it more difficult to provide an assembly structure that can be used in both an upright and an inverted orientation. When a mirror can be used in an inverted orientation it makes the mirror suitable for mounting on either side of the vehicle in those instances where the mirror has desirable aerodynamic features that make it asymmetrical.